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In this study, a probabilistic model within the dislotwin constitutive framework of DAMASK (the Düsseldorf Advanced Material Simulation Kit) was established to describe the cyclic loading behaviors of AZ31B magnesium alloys. Considering the detwinning procedure within the twinned region, this newly developed dislocation–twinning–detwinning model was employed to accurately simulate stress–strain behaviors of AZ31B magnesium alloys throughout tension–compression–tension (T-C-T) cycle loading. The investigations revealed that the reduction in yield stress during the reverse loading process was attributed to the active operation of twinning and detwinning modes. Furthermore, the evolution of the twin volume fraction during cycle loading scenarios was quantitatively determined. According to these results, the relative activities of plastic deformation modes during T-C-T loading were further analyzed. [ABSTRACT FROM AUTHOR]

In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress σ RD : σ ND = 2:1 was higher than that of the ND yield stress under stress ratio σ RD : σ ND = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases. [ABSTRACT FROM AUTHOR]

Ultrasonic welding, known for its severe plastic deformation, faces the challenge of balancing sufficient deformation at the welding interface with minimizing damage to the substrate. This study utilizes the anisotropic deformation mechanisms and mechanical properties of nanotwinned Cu (nt-Cu). Specifically, Cu coatings featuring nanotwin layers aligned parallel to the ultrasonic vibration direction were employed as interlayers in ultrasonic welding of Cu-Cu joints. The effects of the nt-Cu interlayer on the welding quality and the deformation mechanisms under the various welding pressures are investigated. Experimental and molecular dynamics simulations demonstrate that at low welding pressures, the nt-Cu interlayer undergoes deformation and detwinning primarily through twin boundary migration. This mechanism effectively mitigates work hardening during the welding process, localizes deformation at the welding interface, and significantly enhances the strengths of the Cu-Cu joints. The maximum enhancement proportion occurs at a welding pressure of 8 psi, up to 26.75% compared to conventional coarse-grained copper. As the welding pressure increases, the strengthening effect gradually weakens. The deformation mechanism of nt-Cu transitions to dislocation transverse and threading. The interaction between dislocations and twin boundaries forms incoherent twin boundaries and 9R phases, resulting in work hardening of the interfacial regions and reduction of the strengthening effect.

Magnesium alloys are an ideal material for creating lightweight and durable modern transport systems, but their widespread use is limited due to some physical and chemical properties. This paper considers the effect of nonlinear elastic unloading of the MA14 (ZK60, Mg–5.4Zn–0.5Zr) magnesium alloy in a coarse-grained state after recrystallisation annealing. The study found that the nonlinearity of the unloading characteristic, is formed when reaching a certain threshold stress level. It is expected that the effect under the study is associated with the deformation behavior of the alloy, during which the twin structure formation according to the tensile twinning mechanism is observed. The sample material microstructure was determined, by scanning electron microscopy using electron backscattered diffraction analysis. Determination of the threshold stress, for the formation of unloading nonlinearity was carried out by two methods: 1) by the value of the loop area formed by the nonlinearity of the unloading mechanical characteristics and the repeated loading (mechanical hysteresis) characteristics, and 2) by analysing the acoustic emission recorded during failure strain. A comparison of the results obtained, allows suggesting that the unloading nonlinearity is caused by twinning in grains, in which an unfavorable configuration (low Schmidt factor), for dislocation slip is observed. Rotating the twinned crystal at an angle close to 90° does not contribute to an increase in the Schmidt factor and activation of dislocation slip systems to secure the deformed structure through the dislocation strengthening mechanism. With a subsequent decrease in the external stress, detwinning and partial restoration of the crystal lattice configuration occur.

To explore the effect of the precipitated phase particles and twins on the microstructure evolution and neutral layer evolution during bending, {10–12} tensile twins were introduced along the transverse direction (TD) on AZ80 Mg alloy sheets at room temperature. Then pre-compressed samples were aged to induce more precipitations. The reverse tensile tests were carried out at room temperature, and the three-point bending deformation was carried out at 100 °C. After aging treatment, precipitations increased. The results showed that twin crystals can promote precipitation formation. And the YS (yield strength) values of the pre-twinned aged samples were significantly larger than that before aging. During the bending process on the pre-compressed samples, the outside of the sample was dominated by the detwinning behaviors, while the inside region was dominated mainly by twinning. For pre-compressed bending samples, the k values were smaller than the initial bending sample. The tension and compression asymmetry in its inner and outer regions was weaker than that of the original bending sample. The existence of precipitations hindered the detwinning behaviors in outside the pre-twinning aged bending samples, and the twinning in inner region was restrained as well so that the inner and outer tension asymmetry decreased. The k values were smaller than that of the unaged samples, which was beneficial to weaken the bending springback of Mg alloy sheets.

Twinning is an important mechanism for coordinated plastic deformation of magnesium alloys. Pre-setting {10–12} extension twins into magnesium alloy will change the orientation of c-axis of grains and eliminate anisotropy, improving the plasticity and ductility of the alloy. The grains are refined to improve the mechanical properties of the alloy such as yield strength, tensile strength and hardness. Therefore, {10–12} extension twinning in magnesium alloys is becoming more and more popular among magnesium alloy researchers. Many scholars have used electron backscattering diffraction and transmission electron microscope to characterize the internal structure, twin tip and the interaction between twins and precipitate phases of pre-strained magnesium alloys. It was found that {10–12} extended twins can not only weaken the strength of texture, but also change the texture type. The existence of precipitates can not only hinder the growth of twin tip, but also produce stress concentration around it, which promotes the nucleation of new twin variants. Pre-twinning in magnesium alloys can improve the compressive yield stress, but reduce the ultimate compressive strength. In this paper, the mechanism of nucleation and growth of {10–12} extension twins in magnesium alloys, {10–12} extension twins and textures, precipitate, interaction of mechanical properties and the detwinning behavior of {10–12} extension twins are reviewed. Finally, the future development of {10–12} extension twins in wrought magnesium alloys is prospected, and some suggestions are put forward, achieving the aim of providing some reference for further research on the twinning transformation of magnesium alloys. [ABSTRACT FROM AUTHOR]

Magnesium alloys, being the lightest structural metals, have garnered significant attention in various fields. The characterization of inelastic behavior has been extensively investigated by researchers due to its impact on structural component performance. However, the occurrence of twinning in the absence of any applied driving force during unloading has lacked reasonable explanations. Moreover, the influence of deformation mechanisms other than twinning on inelastic behavior remains unclear. In this study, uniaxial tension and compression tests were conducted on hot-rolled magnesium alloy plates, and neutron diffraction experiments were employed to characterize the evolution of macroscopic mechanical response and microscopic mechanisms. Additionally, a twinning and detwinning (TDT) model based on the elastic visco-plastic self-consistent (EVPSC) model has been proposed, incorporating back stress to describe the deformation behavior during stress relaxation. This approach provides a comprehensive understanding of the inelastic behavior of magnesium alloys from multiple perspectives and captures the influence of microscale mechanisms. A thorough understanding of the inelastic behavior of magnesium alloys and a reasonable explanation for the occurrence of twinning under zero-stress conditions offer valuable insights for the precise design of magnesium alloy structures. [ABSTRACT FROM AUTHOR]

Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4% (±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at -2% strain gradually increased from 26.3% to 43.5%; the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number; and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of -component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.

Nanotwinned Ni-Mo-W alloys possess a combination of unique mechanical and thermal properties, such as ultrahigh strength and microstructural stability, which are correlated with the presence of densely packed growth twins. In a previous study, the ultrahigh compressive strength of Ni 84 Mo 11 W 5 (atomic percent) micropillars was associated with the formation of highly localized shear bands, but the trigger for such localized plasticity was not identified. Here, Ni 86 Mo 3 W 11 (atomic percent) micropillars were carefully compressed to various levels to uncover the nanoscale deformation mechanisms that trigger the strain localization. Post-mortem transmission electron microscopy investigations of pillars after the first measurable strain burst revealed ∼50 nm thick shear bands consisting of reoriented and twin-free grains, while the columnar grains adjacent to the shear bands were partly detwinned. More importantly, unlike the Mo-rich pillars, the W-rich pillars showed discernible plasticity before the first strain burst. Close inspection made before the formation of a mature shear band revealed a detwinning region of ∼30 nm thickness that aligned more parallel to the coherent twin boundaries, and multiple nanotwins truncated with incoherent twin boundaries were resolved between the detwinning band and the nanotwinned grains. These observations strongly suggest detwinning, facilitated by migration of incoherent twin boundaries, to be the precursor to strain localization and the intensive shear banding observed in nanotwinned Ni-Mo-W alloys. Comparing the present results with the literature further highlights the general role of detwinning in governing the plastic behavior of nanotwinned alloys with a wide range of stacking fault energy. [Display omitted] [ABSTRACT FROM AUTHOR]

In quenched Fe-C (C: 0.0∼2.0 wt.%) binary alloys, the body-centered cubic (BCC) {112}-type twin structure (density, size and morphology) in martensite was investigated by means of transmission electron microscopy (TEM). In the samples quenched to room temperature, the twin density increased as the carbon content increased. In the carbon-free or pure iron sample, no twin structure was observed. In high carbon martensite, a high density of twins could be seen with twin thickness of 1 nm–2 nm, which is of the scale of the smallest α-Fe grain. The twin density variance is discussed based on a detwinning process, which occurs upon cooling. The twin, as an initial product of martensitic transformation, would experience a higher temperature auto-tempering process in low carbon alloys than in high carbon samples. A noticeable detwinning process takes place in low carbon alloys and results in a low density of twins observed at room temperature. Martensite starting (Ms) temperature plays a crucial role in the detwinning or auto-tempering effect on the twins.

Twinning and detwinning behavior, together with slip behavior, are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction (RD) after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique. The results show that twinning firstly takes place under the compressive strain along the RD. With the increasing compressive strain, {101¯2} tensile twins firstly nucleate, then propagate, and finally thicken. While under a reversed tensile strain along the RD, detwinning occurs. No nucleation happens during detwinning. Thus, tensile twins can detwin at lower tensile strain, followed by thinning, shortening, and vanishing. Slips are also activated to accommodate the plastic deformation. In the matrix, prismatic slip can only dominate at relatively high strains. Otherwise, basal slip dominates. While in the twins, prismatic slip can activate at lower strains, which is ascribed to the texture reorientation.

The nanoscopic deformation of 〈111〉 nanotwinned copper nanopillars under strain rates between 10−5/s and 5 × 10−4/s was studied by using in situ transmission electron microscopy. The correlation among dislocation activity, twin boundary instability due to incoherent twin boundary migration and corresponding mechanical responses was investigated. Dislocations piled up in the nanotwinned copper, giving rise to significant hardening at relatively high strain rates of 3–5 × 10−4/s. Lower strain rates resulted in detwinning and reduced hardening, while corresponding deformation mechanisms are proposed based on experimental results. At low/ultralow strain rates below 6 × 10−5/s, dislocation activity almost ceased operating, but the migration of twin boundaries via the 1/4 〈 10 1 ¯ 〉 kink-like motion of atoms is suggested as the detwinning mechanism. At medium strain rates of 1–2 × 10−4/s, detwinning was decelerated likely due to the interfered kink-like motion of atoms by activated partial dislocations, while dislocation climb may alternatively dominate detwinning. These results indicate that, even for the same nanoscale twin boundary spacing, different nanomechanical deformation mechanisms can operate at different strain rates. [ABSTRACT FROM AUTHOR]

The shape memory effect observed in many alloys arises due to stress induced transformation between variants of the martensitic phase. It is difficult to study this process in detail using continuum approaches and particle based methods are eminently more suitable. In this work, we study detwinning, which is the transformation between martensite variants due to applied stress using a novel discrete particle model. The approach uses a novel multibody interparticle interaction defined directly using a non-convex free energy potential pertinent to such material behavior. This model is able to describe simultaneously occurring multiple microscale events during the detwinning process: nucleation and propagation of ledges along twin boundary. Due to these underlying microscale events the plateau region of stress–strain response shows a jerky nature. The effect of temperature and morphology on the stress–strain behavior of the self-accommodated martensite microstructure is studied in detail. From the simulations, we identify the morphological features affecting the transformation stress for detwinning. The critical parameters are found to be the length and number of twin and macro-twin boundaries and the number of mobile ledges. [ABSTRACT FROM AUTHOR]

Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4% (±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at -2% strain gradually increased from 26.3% to 43.5%; the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number; and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of -component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy. [ABSTRACT FROM AUTHOR]

{332}<113> twinning is an important deformation mode for metastable β–Ti alloys. However, little is known on the reverse detwinning process and its hardening effect. Herein, detwinning behavior in Ti–15Mo alloy and its effect on the microstructure evolution and yield strength is investigated. Twins are generated during pre‐tension along the rolling direction. Then, the pre‐twinned samples are compressed in the same direction by different strains. It is shown that compressive yield strength is significantly improved by pre‐tension compared with the as‐received alloy. Microstructure characterization reveals that almost all the twins generated in pre‐tension were detwinned during the reverse compression. New twins appear in some β grains by increasing the compression strain. The variant with the highest Schmid factor (SF) is likely selected for twinning. Some paired twins formed at grain boundaries do not have the highest SF, but have a large strain compatibility factor (m′), implying a strong influence from local stress. Profuse slip traces are observed, which transferred across the detwinned regions during the reverse compression, causing severe stress concentrations in the primary twin domains. Based on the experimental observations, a possible strengthening mechanism by the twinning–detwinning behavior is proposed and discussed. [ABSTRACT FROM AUTHOR]

Magnesium alloys, being the lightest structural metals, have garnered significant attention in various fields. The characterization of inelastic behavior has been extensively investigated by researchers due to its impact on structural component performance. However, the occurrence of twinning in the absence of any applied driving force during unloading has lacked reasonable explanations. Moreover, the influence of deformation mechanisms other than twinning on inelastic behavior remains unclear. In this study, uniaxial tension and compression tests were conducted on hot-rolled magnesium alloy plates, and neutron diffraction experiments were employed to characterize the evolution of macroscopic mechanical response and microscopic mechanisms. Additionally, a twinning and detwinning (TDT) model based on the elastic visco-plastic self-consistent (EVPSC) model has been proposed, incorporating back stress to describe the deformation behavior during stress relaxation. This approach provides a comprehensive understanding of the inelastic behavior of magnesium alloys from multiple perspectives and captures the influence of microscale mechanisms. A thorough understanding of the inelastic behavior of magnesium alloys and a reasonable explanation for the occurrence of twinning under zero-stress conditions offer valuable insights for the precise design of magnesium alloy structures.

Molecular dynamics method is performed for analyzing the influence of temperature on the compressive loading behavior of nanotwinned Cu. Simulation results show that the plastic deformation mechanism of nanotwinned Cu with 1.88 nm twin thickness is dominated by detwinning behavior, when the temperature is below 220 K. When the temperature is between 250 and 400 K, twin boundaries' migration behavior controls the plastic deformation process. When temperature is below 150 K, twin boundaries have obvious hindrance to dislocations. The hindrance of twin boundaries to dislocations is not apparent above 200 K. In general, low temperatures are more conducive to detwinning behavior. This research provides guidance on controlling detwinning behavior in order to adjust the structure of nanotwinned materials. [ABSTRACT FROM AUTHOR]

Due to their low symmetry in crystal structure, low elastic modulus (∼45 GPa) and low yielding stress, magnesium (Mg) alloys exhibit strong inelastic behaviors during unloading. As more and more Mg alloys are developed, their unloading behaviors were less investigated, especially for rare-earth (RE) Mg alloys. In the current work, the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling. In terms of the stress–strain curves, the inelastic strain, the chord modulus, and the active deformation mechanisms, the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized. The inelastic strains are generally larger under compressive Loading–UnLoading (L–UL) than under tensile L–UL, along the transverse direction (TD) than along the rolling direction (RD) under tensile L–UL, and along RD than along TD under compressive L–UL. The basal slip, twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets.

Magnesium and its alloys have attracted extensive attention due to their favorable mechanical properties, such as low density and high specific strength. The detwinning process of {\begin{document}$10\bar 12$\end{document}} tensile twins subjected to periodic loading is one of the microscopic mechanisms of fatigue damage in magnesium and its alloys. Moreover, self-interstitial atoms (SIAs) widely exist as a typical kind of point defects in metals. The migration, aggregation, and interaction with other defects, of SIAs affect the metal mechanical properties. In this work, molecular dynamics simulation was employed to study the detwinning process of {\begin{document}$10\bar 12$\end{document}} twins under shear loads in magnesium, focusing on the interaction between the twin boundary and SIAs in the detwinning process. A simulation system containing two coherent twin boundaries (CTBs) with periodic boundary conditions applied along the two in-plane directions was adopted. The classic embedded atom method (EAM) interatomic potential developed by Liu et. al was used for simulation accuracy and comparison with other studies. The simulation results show that the SIAs are absorbed by the CTBs and migrate along with them. The absorbed SIAs can be released with the disappearance of the CTBs during the detwinning process. By the SIA adsorption and release, detwinning process will result in a more concentrated SIA distribution. The simulation results reveal that SIAs will be adsorbed by CTB if the distance between the CTB and SIA is less than 0.752 nm at 0 K and 3.59 nm at 273 K. The energy barrier of the adsorption process is also obtained using the nudged elastic band (NEB) method. The SIA spatial distribution changes after the SIA interactions with CTB in detwinning process. Given that the crystal defects such as dislocation loops can be induced by the dense distribution of SIAs at a long timescale, this study clarifies the fatigue mechanical properties of magnesium and magnesium alloys subjected to periodic loading.

Metals with a bimodal grain size distribution have been found to have both high strength and good ductility. However, the coordinated deformation mechanisms underneath the ultrafine-grains (UFGs) and coarse grains (CGs) still remain undiscovered yet. In present work, a bimodal Cu with 80% volume fraction of recrystallized micro-grains was prepared by the annealing of equal-channel angular pressing (ECAP) processed ultrafine grained Cu at 473 K for 40 min. The bimodal Cu has an optimal strength-ductility combination (yield strength of 220 MPa and ductility of 34%), a larger shear fracture angle of 83° and a larger area reduction of 78% compared with the as-ECAPed UFG Cu (yield strength of 410 MPa, ductility of 16%, shear fracture angle of 70°, area reduction of 69%). Grain refinement of recrystallized micro-grains and detwinning of annealing growth twins were observed in the fractured bimodal Cu tensile specimen. The underlying deformation mechanisms for grain refinement and detwinning were analyzed and discussed.

Twinning and detwinning behavior, together with slip behavior, are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction (RD) after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique. The results show that twinning firstly takes place under the compressive strain along the RD. With the increasing compressive strain, { 10 1 ¯ 2 } tensile twins firstly nucleate, then propagate, and finally thicken. While under a reversed tensile strain along the RD, detwinning occurs. No nucleation happens during detwinning. Thus, tensile twins can detwin at lower tensile strain, followed by thinning, shortening, and vanishing. Slips are also activated to accommodate the plastic deformation. In the matrix, prismatic slip can only dominate at relatively high strains. Otherwise, basal slip dominates. While in the twins, prismatic slip can activate at lower strains, which is ascribed to the texture reorientation. [ABSTRACT FROM AUTHOR]

Gradient-structured CoCrFeMnNi high-entropy alloy (HEA) with all grain sizes lying in the inverse Hall-Petch range exhibits a significant synergistic softening behavior, with the yield strength even lower than the rule of mixtures (ROM) under uniaxial tensile loading. The softening of grain boundaries (GB) is very pronounced in hard domains due to the extremely small grain size. Moreover, the coordinated deformation of heterostructure promotes grain rotation in soft domains with large grain sizes. However, the extra strength generated by hetero-deformation induced (HDI) strengthening increases with increasing volume fraction of hard domain, contributing to a gradual decrease in the gap between yield strength and ROM. Here, we identify multiple deformation mechanisms promoted by mechanical incompatibility through molecular dynamics (MD) simulations. On the one hand, the higher volume fraction of the hard domain encourages the adaptation of dislocation-mediated activities to plastic strains, thus reducing the possibility of GB sliding or intergranular brittle cracking. More importantly, soft domains are more susceptible to detwinning under additional compressive stress, which induces grain refinement in localized regions and contributes extra strength. Observation of the strain distribution reveals that the banded shear bands (SBs) are spread throughout the soft domains, which effectively improves strain gradient strengthening. It has been verified that the gradient structure has the highest extra strength at the hard domain volume fraction of 40–50%. The findings provide insights into the engineering applications of gradient-structured HEA. [Display omitted] • GNG-CoCrFeMnNi-HEA in the inverse Hall-Petch range exhibits synergistic softening-strengthening behaviors. • Localized grain refinement of soft domains provides extra strength and excites strain gradient strengthening. • The optimal volume fraction of hard domain for gradient structures to obtain extra strengthening is 40–50%. [ABSTRACT FROM AUTHOR]

To examine the effects of pre-induced precipitations on microstructure evolution and mechanical properties of pre-twinned ZK61 Mg alloy at elevated temperatures, the commercially rolled ZK61 Mg alloy sheets (AR samples) were pre-twinned and {10−12} tensile twins were added (PT samples). Some samples were aged, precipitated phases were introduced (PTA samples), and subsequently uniaxial tensile strain was applied. The results reveal that at elevated temperatures, the interactions of detwinning, dynamic recrystallization (DRX), and precipitation have a distinctive impact on the microstructure evolution. At room temperature (RT) and 100 ℃, strain is dominated by detwinning, while the precipitation phase impedes the detwinning behaviors. DRX influences the evolution of the microstructure at 150 ℃, 200 ℃, and 250 ℃. The presence of precipitated phases promotes recrystallization nucleation. Continuous DRX (CDRX), detwinning, and precipitated phase deformation are coordinated at 150 ℃. DRX in aged samples has a limited effect, while detwinning plays a dominant role. The ultimate tensile strength (UTS) value increment of PTA sample relative to PT sample reaches 31.8 MPa. The deformation is generated by the discontinuous DRX (DDRX) at 250 ℃, and the precipitation and DDRX have a higher impediment on detwinning, resulting in more twins restraining in the PTA sample. The UTS value of PTA sample only increases by 7.7 MPa compared with PT sample. • Precipitation effects detwinning and dynamic recrystallization in ZK61 Mg alloy. • Detwinning and recrystallization compete at elevated temperatures. • VPSC were used to analyze the slip behaviors. [ABSTRACT FROM AUTHOR]

Stress-induced martensitic detwinning and martensitic transformation during step-wise compression in an austenite Ni–Mn–Ga matrix with a martensite cluster under uniaxial loading have been investigated by electron backscatter diffraction, focusing on the crystallographic features of microstructure evolution. The results indicate that detwinning occurs on twins with a high Schmid factor for both intra-plate and inter-plate twins in the hierarchical structure, resulting in a nonmodulated (NM) martensite composed only of favourable variants with [001]NM orientation away from the compression axis. Moreover, the stress-induced martensitic transformation occurs at higher stress levels, undergoing a three-stage transformation from austenite to a twin variant pair and finally to a single variant with increasing compressive stress, and theoretical calculation shows that the corresponding crystallographic configuration is accommodated to the compression stress. The present research not only provides a comprehensive understanding of martensitic variant detwinning and martensitic transformation under compression stress, but also offers important guidelines for the mechanical training process of martensite.

Experimental observations indicate that pre-deformation can influence the mechanical properties of magnesium alloys. However, inconsistent or even contradictory conclusions have been drawn mainly due to the difficulty of isolating an individual influencing factor from those playing interactive roles in an experiment. Therefore, a systematical study in terms of crystal plasticity modeling is performed to evaluate the effect of pre-deformation (pre-rolling and pre-compression) in the current work. The subsequent tensile response of the magnesium alloy AZ31B sheet along the transverse direction and the rolling direction after pre-deformation is simulated. It is found that both pre-rolling and pre-compression can either enhance or deteriorate the mechanical properties of the AZ31B sheet. If annealing is applied, the pre-deformed microstructure is retained and the mechanical properties are generally enhanced. Pre-compression with ~ 3% strain and annealing are able to enhance the overall mechanical properties of a rolled Mg alloy sheet the most. Based on the modeling results, the properties of magnesium alloys can be affected differently with different pre-straining paths, different loading directions, with annealing or without. These findings help us understand the inconsistency in different experimental studies and also reveal the role of pre-deformation and the accompanying influencing factors on the properties of magnesium alloys. [ABSTRACT FROM AUTHOR]

Due to their low symmetry in crystal structure, low elastic modulus (∼45 GPa) and low yielding stress, magnesium (Mg) alloys exhibit strong inelastic behaviors during unloading. As more and more Mg alloys are developed, their unloading behaviors were less investigated, especially for rare-earth (RE) Mg alloys. In the current work, the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling. In terms of the stress–strain curves, the inelastic strain, the chord modulus, and the active deformation mechanisms, the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized. The inelastic strains are generally larger under compressive Loading–UnLoading (L–UL) than under tensile L–UL, along the transverse direction (TD) than along the rolling direction (RD) under tensile L–UL, and along RD than along TD under compressive L–UL. The basal slip, twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets. [ABSTRACT FROM AUTHOR]

The mechanism of radiation-induced detwinning is different from that of deformation detwinning as the former is dominated by supersaturated radiation-induced defects while the latter is usually triggered by global stress. In situ Kr ion irradiation was performed to study the detwinning mechanism of nanotwinned Cu films with various twin thicknesses. Two types of incoherent twin boundaries (ITBs), so-called fixed ITBs and free ITBs, are characterized based on their structural features, and the difference in their migration behavior is investigated. It is observed that detwinning during radiation is attributed to the frequent migration of free ITBs, while the migration of fixed ITBs is absent. Statistics shows that the migration distance of free ITBs is thickness and dose dependent. Potential migration mechanisms are discussed.

The present study investigated the influences of Dy-addition on the microstructural characterization, functional behaviour and deformation mechanisms in high-temperature Ni54Mn25Ga21 alloys. The results indicated that adequate Dy-addition contributed to a desirable trade-off among compressive strength, ductility and functional performance. Ni54Mn25Ga20.9Dy0.1 alloy showed the highest shape memory recoverable strain due to the improvement of mechanical properties and formation of small Dy-rich precipitates. Meanwhile, an obvious pseudoelasticity was observed over a wide temperature range with a maximum recoverable strain of 3.74% at 320°C in this alloy. All the Dy-containing alloys exhibited low thermal hysteresis. However, it was revealed that an abnormal relationship between thermal hysteresis and middle eigenvalue λ 2 existed for the investigated alloys with a lattice transition from cubic to tetragonal. [ABSTRACT FROM AUTHOR]

We investigate the onset of detwinning in magnesium alloy Mg-3Al-1Zn under continuous loading with real-time in situ synchrotron X-ray diffraction. Detwinning of the { 10 1 ¯ 2 } extension twins activated both by tension parallel to and compression perpendicular to the c -axis fibers is explored. The experimental results reveal that detwinning of the { 10 1 ¯ 2 } extension twins occurs immediately upon unloading, regardless of whether the twins are activated by tension parallel to or compression perpendicular to the c -axis fibers. [ABSTRACT FROM AUTHOR]

Via in-situ experiments, we show the atomic-scale evolution of incoherent twin boundary (ITB) into a high-angle grain boundary (HAGB). We find that the electron-beam can activate the motion of Shockley partials, which causes detwinning and formation of segmented ITB (sITB). Consequently, a series of step-like extended dislocations are further produced along the sITB due to the Shockley partial cross-slip on two intersecting {111} planes. This process results in an unfixed misorientation (<18°) between the original twins and the un-detwinned parts, and further converts the sITB into a HAGB. The study offers insights into the atomic-scale grain refinement in nano-twinned materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The detailed deformation mechanism and its microstructural modifications of white cast iron grinding balls used in comminution have been investigated using transmission electron microscopy (TEM) and XRD. De-shaping is the primary mode of ball consumption, and fracture of balls is a relatively uncommon failure mode. Deshaping is the manifestation of abrasive wear caused during the operation, and abrasive wear is accompanied by microstructural changes. Micro-cutting is the foremost mechanism. The original microstructure of the matrix of unused grinding balls was observed to have twinned martensite with ω phase with an orientation relation of M-(1 2 ¯ 1)//T-( 1 ¯ 2 1 ¯ ) and { 1 ¯ 1 ¯ 3 }M//{11 3 ¯ }T and M-(1 2 ¯ 10)//ω(0 1 ¯ 10) and { 1 ¯ 1 ¯ 3 }M//{1 2 ¯ 1 3 ¯ }ω. However, the presence of unstable ω phase, located at the twinning boundary, causes detwinning and forms lath martensite during tempering caused by localized heat during abrasion. Nano-cementite is formed at lath boundaries. Some cracking was observed, but the crack orientation is radial, indicating a response to tangential stresses associated with abrasion as opposed to dynamic stress waves from high-angle impact. Tangential tensile stresses due to surface traction during the abrasion process lead to radial cracks in brittle eutectic carbides, which join up and cause material removal. [ABSTRACT FROM AUTHOR]

This study investigates the effect of annealing temperature on the microstructure, deformation behavior, and mechanical properties of a rolled AZ31 alloy having {10–12} twins. To this end, rolled AZ31 samples are precompressed to 6.0% along the rolling direction (RD) to introduce {10–12} twins and then are annealed at 200, 250, and 300 °C for 1 h. The results reveal that as the annealing temperature increases, the grain size of the annealed samples increases and their RD-oriented basal texture is strengthened. In addition, the number of {10–12} twin boundaries gradually decreases and they almost disappear after annealing at 300 °C. Under tension along the RD, the predominant deformation mechanism of the annealed samples changes from detwinning of preexisting twins to {10–12} twinning as the annealing temperature increases. The annealed samples exhibit different tensile strengths and elongations according to the annealing temperature. Particularly, the tensile elongation increases by 56%, from 13.2% to 20.6%, as the annealing temperature increases from 200 to 300 °C. The variations in the mechanical properties of the annealed samples with the annealing temperature are discussed in detail on the basis of their microstructural characteristics and deformation behaviors. [Display omitted] • A rolled AZ31 alloy is compressed to 6% and then annealed at 200, 250, and 300 °C. • The activation of SIBM during annealing enhances with increasing annealing temperature. • Tensile deformation mechanism of annealed materials varies with annealing temperature. • It changes from detwinning (200) to detwinning + twinning (250) and twinning (300). • Tensile elongation of annealed materials gradually increases with annealing temperature. [ABSTRACT FROM AUTHOR]

Annealing of deformed metals is considered as a process which necessarily leads to softening, due to the annihilation of lattice defects. However, in laminated materials, annealing at moderate temperatures may induce hardening. In this study, a laminated structure at two sides of the sample is produced by ultrasonic introduced intermittently for 15 min, during the electrodeposition process. For comparison, a sandwich structure is prepared under ultrasonic without interruption at two sides of the sample. All the samples are annealed for 30 min at 373 K, 473 K and 573 K. The common softening after annealing is observed for the sample without laminated structure in the two sides. However, for the other sample that possesses laminated structure in the same area at the two sides, the strength and ductility increase rather than decrease after annealing. The sample that possesses laminated structure in the same area at the two sides annealed at 373 K shows an evident change, which increases in σ _0.2 from 299 to 353 MPa, in σ _UTS from 477 to 533 MPa, and in ε _ue from 7.6% to 9.5%. According to the XRD results, annealing-induced hardening is not attributable to occurring phase transformation. Detailed microstructural TEM results demonstrate that the annealing-induced hardening is attributed to the surface laminated interfaces and high-density growth twins in interfacial transition zones. In addition, the detwinning occurred during subsequent tensile deformation, also plays a crucial role.

The presence of complex states-of-stress and strain-rates directly influence the dominant deformation mechanisms operating in a given material under load. Mg alloys have shown limited ambient temperature formability due to the paucity of active slip-mechanisms, however, studies have focused on quasi-static strain-rates and/or simple loading conditions (primarily uniaxial or biaxial). For the first time, the influence of strain-rate and stress-triaxiality is utilized to unravel the active deformation mechanisms operating along the rolling, transverse- and normal-directions in wrought AZ31-alloy. It is discovered that the activation of various twin-mechanisms in the presence of multiaxial loading is governed by the energetics of the applied strain-rates. IMPACT STATEMENT It is shown for the first time that the higher deformation energy associated with dynamic strain-rates, coupled with high-triaxiality, promotes detwinning and texture evolution in HCP alloys with high c/a ratio.